A Bluetooth system provides a communication channel between two electronic devices via a short-range radio link. In particular, the Bluetooth system operates in the radio frequency range around 2.45 GHz in the unlicensed Industrial-Scientific-Medical (ISM) band. The Bluetooth radio link is intended to be a cable replacement between portable and/or fixed electronic devices. The portable devices include mobile phones, communicators, audio headsets, laptop computers, other GEOS-based or palm OS-based devices and devices with different operating systems.
The Bluetooth operating frequency is globally available, but the permissible bandwidth of the Bluetooth band and the available RF channels may be different from one country to another. Globally, the Bluetooth operating frequency falls within the 2400 MHz to 2497 MHz range. In the U.S. and in Europe, a band of 83.7 MHz bandwidth is available, and the band is divided into 79 RF channels spaced 1 MHz apart. Bluetooth network arrangements can be either point-to-point or point-to-multipoint to provide connection links among a plurality of electronic devices. Two to eight devices can be operatively connected into a piconet, wherein, at a given period, one of the devices serves as the master while the others are the slaves. Several piconets may form a larger communications network known as a scatternet, with each piconet maintaining its independence. The baseband protocol for a Bluetooth system combines circuit and packet switching. Circuit switching can be either asynchronous or synchronous. Up to three synchronous data (logical) channels, or one synchronous and one asynchronous data channel, can be supported on one physical channel. Each synchronous channel can support a 64 Kb/s transfer rate while an asynchronous channel can transmit up to 721 Kb/s in one direction and 57.6 Kb/s in the opposite direction. If the link is symmetric, the transfer rate in the asynchronous channel can support 432.6 Kb/s. A typical Bluetooth system consists of a radio link, a link control unit and a support unit for link management and host terminal interface functions. The Bluetooth link controller carries out the baseband protocols and other low-level routines. Link layer messages for link set-up and control are defined in the Link Manager Protocol (LMP). In order to overcome the problems of radio noise interference and signal fading, frequency hopping is currently used to make the connections robust.
Currently, each of the 79 RF channels is utilized by a pseudo-random hopping sequence through the Bluetooth bandwidth. The hopping sequence is unique for each piconet and is determined by the Bluetooth device address of the master whose clock is used to determine the phase of the hopping sequence. The channel is divided into time slots of 625 μs in length and numbered according to the master clock, wherein each time slot corresponds to an RF hop frequency, and wherein each consecutive hop corresponds to a different RF hop frequency. The nominal hop rate is 1600 hops/s. All Bluetooth devices participating in the piconet are time and hop synchronized to the channel. The slot numbering ranges from 0 to 227−1 and is cyclic with a cycle length of 227. In the time slots, master and slave devices can transmit packets. Packets transmitted by the master or the slave device may extend up to five time slots. The RF hop frequency remains fixed for the duration of packet transmission.
The ISM frequency bands can be used by many different devices, which include wireless local area networks (WLANs), microwave ovens, and lighting equipment. The interference caused by these multiple different applications is inherent to almost any device, which is connected to the piconet. Currently, the usage of ISM frequency bands is growing very fast. In order to survive in these frequency bands, new wireless communication systems must utilize a robust modulation scheme with a certain method of channel allocation. For example, WLAN systems are using a Frequency Hopping Spread Spectrum (FHSS) method, in which transmission takes place only a short time in each channel, and Direct Sequence Spread Spectrum (DSSS) modulation, which overcomes narrow-band interference by spreading. However, in these systems the allocation of channels, or channelization, is organized by using either a carrier sensing (CS) method or a Code Division Multiple Access (CDMA) method. In the CS method, each of the channels which are to be used are measured in order to determine whether a transmission is taking place in that channel. If the channel under measurement does not have an ongoing transmission, then the channel can be used for hopping. The major problem with the carrier sensing method is that the measurement is ineffective for the traffic type that uses a different modulation method. In the CDMA method, while the narrow-band interferer is spread in the receiver, the received noise is actually increased, thereby reducing the noise margin of the system. Optionally, it is also possible to establish virtual traffic channels by using different hopping frequencies. However, this does not avoid the parts of the spectrum where the interference occurs.
It is advantageous and desirable to provide a method and system for making connections between devices operating in the ISM bands by effectively avoiding the parts of the spectrum where channel conditions such as interference and noise levels may adversely affect the channel connection.